The present invention relates generally to a package rotary seal assembly and more particularly to such an assembly having an improved stationary seal seat which can be operated without lubrication at the seal face.
Rotary seals are well known in the art and the present invention represents an improvement in the type of rotating package seals generally disclosed in U.S. Pat. No. 3,582,092. In the type of package rotary seal illustrated in that patent, the stationary seal seat, historically, has been produced from either of two materials. One of these materials was a high density, hard ceramic, such as alumna, tungsten carbide, silicon carbide or the like. Such high density ceramics provide good corrosion resistance and a hard non-wearing surface which can be lapped to a smooth finish at the seal face. Such a material has its drawbacks, however, in that it is brittle and susceptible to breakage during mounting of the seal and care must be exercised when clamping the seal in place. Also non-metallic seats are relatively expensive in large sizes.
A second material employed as the stationary seat has been a glass or crystalized glass coated stainless steel. The glass coated stainless steel provides a less expensive seal seat in the larger sizes and a rugged seal which is not easily damaged during mounting. On the other hand, the glass or crystalized glass coating provides a seal surface which is inferior to the high density, hard ceramic.
In the present invention, the desirable features of both types of seals are combined to provide a stationary seal member which has a hard ceramic, non-wearing sealing surface combined with a glass or crystalized glass coated stainless steel mounting ring.
Another disadvantage of prior art package seals is that for most applications a lubricant must be applied at the seal faces. Otherwise there is excessive wear of the rotating seal member and often an undesirable build-up of heat. While systems are known for lubricating and cooling the rotating seal there are various applications where it is desirable to run the seal without a lubricant. For example, in pharmaceutical applications, there must be no leakage of a contaminant, such as a lubricant, into the pharmaceutical mixture being prepared. Accordingly, mechanical rotating seals for vessels used to produce pharmaceuticals are usually run dry to eliminate the likelihood of contamination by leakage of the lubricant into the process. However, because the seals are operated dry, rotational speeds must be kept to a minimum to minimize wear on the rotating element of the seal and to prevent excessive heat buildup at the seal face which could ignite vapors generated during production of the pharmaceutical.
The present invention, then, provides a stationary seat for a rotating mechanical seal which can be run dry at a reasonable speed with minimum wear and heat generation. Such a seal, while being useful for a wide variety of applications, finds primary utility in the manufacture of pharmaceuticals and food stuffs.